Lithium ion batteries are widely used as power sources because they provide high power with low resistance. Defects in performance stem from hindered Li+ diffusion at the interface between the positive electrode and electrolyte. Lithium ion batteries are used in a broad range of applications and are currently being used to power the next-generation of electric vehicles. However, state-of-the-art lithium ion electrode materials do not meet, simultaneously, the criteria for high power, high energy, and long life necessary for transportation applications. Lithium ion batteries are limited in the energy they can practically deliver due to surface reactivity, i.e., electrode/electrolyte interactions. Surface changes become a significant factor in cell degradation much earlier than bulk structural changes of electrode materials.
A major challenge for all lithium ion chemistries is the degradation of electrode-particle surfaces under high-voltage/high-energy operation. Serious degradation phenomena involve the interaction of oxidized transition metals (TMs) with organic electrolytes leading to surface-film deposition, TM dissolution, the release of oxygen, and subsequent reorganization of surface layers. These mechanisms lead to a loss of available lithium, a decrease in the power and energy of cells, and a decrease in the cycle life of cells.
Typical surface protection strategies involve the use of a physical barrier to isolate the electrode surface from the electrolyte. These physical barriers can still be etched by the electrolyte, crack, separate from the surface, and cause increased impedance. There is an ongoing need for improving electrode surface stability, thus, improving power and energy capabilities as well as extending cycle life in lithium ion batteries. The materials disclosed herein address this need.